The present invention is directed to a reverse current protection circuit and, more particularly, to a reverse current protection circuit capable of protecting a switch circuit from reverse current damage.
Generally, reverse currents are generated in a device when a voltage at an output terminal of the device is higher than a voltage at an input terminal of the device. The reverse currents flow back from the output terminal to the input terminal, which may decrease performance or even damage the device. Therefore, many devices have reverse current protection circuitry.
In a switch circuit, a conventional reverse current protection circuit sets a voltage reference that is equal to the voltage at the input terminal of the switch circuit. When the voltage at the output terminal of the switch circuit is higher than the voltage reference, the conventional reverse current protection circuit generates a RCP (reverse current protection) signal to disconnect the output terminal of the switch circuit from the input terminal of the switch circuit. However, since the voltage reference generally has a certain fluctuation range, reverse currents may have already occurred when the voltage at the output terminal of the switch circuit is higher than the voltage reference. Thus the conventional reverse current protection circuit does not provide the switch circuit with timely and effective protection from reverse currents.
Setting the voltage reference to be lower than the voltage at the input terminal of the switch circuit causes a different problem. When the switch circuit starts up or a load on the switch circuit changes, an overshoot voltage occurs at the output terminal of the switch circuit. Generally, the overshoot voltage is a ripple voltage, and a level of the ripple voltage gradually decreases. When the conventional reverse current protection circuit disconnects the output terminal of the switch circuit from the input terminal of the switch circuit, the overshoot voltage is pulled down to a very low level. When the output voltage is pulled down to be lower than a predetermined level, the input terminal and the output terminal of the switch circuit reconnect. Then, the ripple voltage occurs again at the output terminal of the switch circuit and rapidly rises up to an original level of the overshoot voltage occurring when the switch circuit starts up or the load of the switch circuit changes, and the reverse current protection circuit causes the overshoot voltage to be pulled down to a very low level again. Thus, the conventional reverse current protection circuit causes the output voltage of the switch circuit to be very unstable during start-up and load changes.
Accordingly, it is desired to have a reverse current protection circuit that can both make the output voltage of the switch circuit more stable and protect the switch circuit from reverse current damage during start-up and load changes.